Colistin and tigecycline resistance in carbapenemase‐producing Gram‐negative bacteria: emerging resistance mechanisms and detection methods

A literature review was undertaken to ascertain the molecular basis for tigecycline and colistin resistance mechanisms and the experimental basis for the detection and delineation of this resistance particularly in carbapenemase‐producing Gram‐negative bacteria. Pubmed, Google Scholar and Science Direct were searched with the keywords colistin, tigecycline, resistance mechanisms and detection methods. Trans‐complementation and comparative MIC studies, mass spectrometry, chromatography, spectrofluorometry, PCR, qRT‐PCR and whole genome sequencing (WGS) were commonly used to determine tigecycline and colistin resistance mechanisms, specifically modifications in the structural and regulatory efflux (acrAB, OqxAB, kpgABC adeABC‐FGH‐IJK, mexAB‐XY‐oprJM and soxS, rarA robA, ramRAB marRABC, adeLRS, mexRZ and nfxb) and lipid A (pmrHFIJFKLM, lpxA, lpxC lpxD and mgrB, pmrAB, phoPQ,) genes respectively. Mutations in the ribosomal 16S rRNA operon rrnBC, also yielded resistance to tigecycline through target site modifications. The mcr‐1 gene conferring resistance to colistin was identified via WGS, trans‐complementation and a murine thigh infection model studies. Common detection methods are mainly antibiotic sensitivity testing with broth microdilution while molecular identification tools are mostly PCR and WGS. Spectrofluorometry, MALDI‐TOF MS, micro‐array and real‐time multiplex PCR hold much promise for the future as new detection tools.     

Survivorship of a declining population of southern elephant seals, Mirounga leonina, in relation to age, sex and cohort

This study quantified both the age- and sex-specific survival rates of juveniles and adults, and tested for interannual differences in age-specific survival rates of the southern elephant seal population at Marion Island. Pups were tagged on an annual basis from 1983 onwards at Marion Island, and a consistent recapture program yielded data that was analysed using the software package MARK to obtain maximum-likelihood estimates of survival and capture probability. On average, 1st-year survival was 0.58 and 0.62, and survival rate averaged over the first 3 years of life, 0.69 and 0.74 for males and females, respectively. From years 4 to 9, the average survival rate was 0.66 and 0.75 for males and females, respectively. Survival estimates for elephant seals in their 10th–13th year are also presented, although these are based on very small sample sizes. Averages of age-specific survival estimates from the earlier (mostly 1983–1987 cohorts) and later (mostly 1988–1992 cohorts) periods were compared and considerable reductions were observed in 4th- and 5th-year male survival, and 4th-year female survival. The comparatively low adult survival is suggested as the proximate cause, and food limitation as deduced from the decline in survival of elephant seals with comparatively high energetic demands as the ultimate cause behind the population decline at Marion Island. Although not tied in with the decline of the population, 1987, 1990 and 1993 were identified as high-mortality years. Received: 14 December 1998 / Accepted: 14 June 1999     

First-year survival of southern elephant seals,Mirounga leonina,at sub-Antarctic Macquarie Island

Juvenile seals branded on the isthmus of Macquarie Island as pups displayed a high degree of philopatry. They returned more often and in greater densities to the northern third of the island within 10 km of their birth sites. Juvenile seals were observed to haul out more frequently and in greater numbers on the east coast as opposed to the west. Juvenile seals typically hauled out on two occasions, once during the winter, and once to moult. The probability of recapturing (resighting) branded and tagged seals was greater during the mid-year haulout. First-year survival estimates were obtained from searches of all Macquarie Island beaches for marked (branded and tagged) seals. From a branded population of 2000 seals, 897 were known to be alive at age 1 year, and minimum first-year survival was calculated at 44.85%. To this minimum estimate was added the number of seals overlooked during systematic and standardised searches of the island, and a revised estimate of 65.60% was calculated. Survival rates calculated using a custom model and a conventional mark-recapture model (MARK) were compared and no differences detected. Actual survival data and probability of sighting estimates were included in the revised estimate of first-year survival of southern elephant seals at Macquarie Island. There were no differences in the number of surviving males and females. Accepted: 25 October 1998     

Species identification and comparative population genetics of four coastal houndsharks based on novel NGS‐mined microsatellites

The common smooth‐hound (Mustelus mustelus ) is the topmost bio‐economically and recreationally important shark species in southern Africa, western Africa, and Mediterranean Sea. Here, we used the Illumina HiSeq? 2000 next‐generation sequencing (NGS ) technology to develop novel microsatellite markers for Mustelus mustelus . Two microsatellite multiplex panels were constructed from 11 polymorphic loci and characterized in two populations of Mustelus mustelus representative of its South African distribution. The markers were then tested for cross‐species utility in Galeorhinus galeus , Mustelus palumbes , and Triakis megalopterus , three other demersal coastal sharks also subjected to recreational and/or commercial fishery pressures in South Africa. We assessed genetic diversity (N _A, A _R, H _O, H _E, and PIC) and differentiation (F _ST and D _est) for each species and also examined the potential use of these markers in species assignment. In each of the four species, all 11 microsatellites were variable with up to a mean N _A of 8, A _R up to 7.5, H _E and PIC as high as 0.842. We were able to reject genetic homogeneity for all species investigated here except for T . megalopterus . We found that the panel of the microsatellite markers developed in this study could discriminate between the study species, particularly for those that are morphologically very similar. Our study provides molecular tools to address ecological and evolutionary questions vital to the conservation and management of these locally and globally exploited shark species.     

Multiple origins of vagrant Subantarctic fur seals: a long journey to the Brazilian coast detected by molecular markers

In this study, we present the first data about putative source populations of the vagrant Subantarctic fur seal, Arctocephalus tropicalis, found on the Brazilian coast, through the comparison of their mitochondrial DNA control sequences to exclusive haplotypes from the main breeding colonies of the species. The results indicated that, despite the majority of the vagrant individuals are from Gough Island (the closest breeding site to the Brazilian coast), they also come from other reproductive colonies, such as Crozet Island, a distance around 16,500 km from the Brazilian coast. Furthermore, the molecular data identified three possible management units: (1) Gough, (2) Amsterdam, and (3) Marion, Macquarie and Crozet. This significant genetic subdivision must be taken into account in any future management plan for the species conservation, including rehabilitation and even reintroduction of vagrant fur seals. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Germination of <i>Eryngium regnellii</i>: a major species for ecological restoration of plant-pollinator interactions in the Southern Pampas (Buenos Aires,Argentina)

Eryngium regnellii Malme belongs to the largest genera in the Apiaceae family, with 250 species worldwide and 65 represented in South America. It is a herbaceous species typical of hill plant communities, which, along with remnant grassland patches, are the most relevant natural habitats for the maintenance of diversity in the Southern Pampas. Eryngium regnellii is key to the maintenance of pollination mutualisms, being a generalist (displaying a diverse assemblage of pollinators) and ubiquitous species (present in all studied sierras). However, fragmentation of the Pampean landscape due to agricultural intensification has led to the loss of natural environments. Therefore, the reintroduction of E. regnellii in strategic places would facilitate the occurrence of wild pollinators, while favoring pollination services in the agroecosystem. The germination requirements of E. regnellii were studied because a better knowledge of the reproductive biology of this species would provide information relevant to its reproduction and reintroduction into degraded areas. Germination percentages and mean time to germination were evaluated, using one control and two pre-germination treatments: chemical scarification with sulfuric acid, and mechanical scarification with sand paper. Chemical scarified seeds did not germinate. Mechanically scarified and control seed groups showed no significant differences either in germination percentages (49% and 59% respectively) or in mean germination time (13 and 14 days, respectively). Results indicate that E. regnellii shows no physical dormancy, and does not require specific pre-germination treatments for germination under the studied laboratory conditions. The high germination capacity of E. regnellii, along with its ecological attributes, make it a potential species for restoring plant-pollinator interactions in the fragmented landscapes of the Southern Pampas.     

Nitrate reductase activity,biomass, yield,and quality in cotton in response to nitrogen fertilization

In the production of cotton (Gossypium hirsutum L.), nitrogen fertilization is one of the most costly crop practices, but important to reach high yields. However, high nitrogen (N) content in plants does not always translate into a high fibre production. One way of assessing the efficiency of the N fertilizer is through the enzymatic activity of the nitrate reductase (NR). This is a key enzyme in N assimilation, whose activity is regulated by a number of endogenous and exogenous factors that determine yield. The aim of this study was to assess the effect of N fertilization on yield, fibre quality, biomass, and NR enzymatic activity in vivo in the cotton variety Fiber Max 989. The evaluated application rates were 0, 50, 100, and 150 kg/ha of N, using urea as a source (46% N) in a randomizedblock design with three replicates. At harvest, the maximum yield of seed cotton and the greatest accumulation of total foliar biomass through time was reached after applying 150 kg N/ha. The different N-application rates did not affect the components of cotton-fibre quality. The activity of endogenous NR was greater on plants where 150 kg N/ha were applied. The highest cotton yield and N contents were obtained on these plants. Therefore, the NR activity in vivo could be used as a bioindicator of the N nutritional level in cotton.